Recently there has been a trend in replacing conventional incandescent light bulbs with LED bulbs. The replacement of conventional incandescent light bulbs with one or more LEDs is desirable because incandescent bulbs are inefficient relative to LEDs, e.g., in terms of energy use and longevity.
LED bulbs also offer the possibility to employ two or more groups or “channels” of LEDs which produce light of different colors, each controllably supplied with predetermined currents to enable the generation and mixing of light to produce general illumination with desired attributes or a desired lighting effect. Thus, LEDs offer more versatile lighting solutions.
While it is desirable to replace incandescent light bulbs with LEDs, there are many lighting fixtures, however, where replacement is difficult because of the operating conditions. In particular, heat management is critical. For example, in domestic lighting applications, a bulb is often recessed into a housing. This is particularly the case for spot lamps.
The standard solution is to provide heat sinking structures for dissipating excess heat.
The price of LED-based bulbs has reached a level that makes it affordable for consumers. There is however fierce competition among manufacturers of these bulbs, and a huge pressure to reduce the cost price of the bulbs. Despite recent cost reductions, LED bulbs are still relatively expensive. This is mainly the result of the price of the components such as the heat sinks, the LEDs, the driver, the printed circuit board (PCB), as well as the cost associated with mounting the components.
A reduction in cost price is made possible for example by using a light source in the form of a linear array of electrically connected LEDs on a thin and narrow flexible substrate. In this way, the LEDs can be mounted (soldered) in a continuous linear process. During the process, also a phosphor can be applied (e.g. by dip-coating and drying). Afterwards, the long line of LEDs can be cut to length.
The length then determines the light output of the bulb. The main problem with this proposition is that such a line of LEDs is difficult to cool.
What is needed is a LED lamp that can be manufactured at low cost but which can also efficiently dissipate heat, and without requiring costly heat sinking structures. However, in the absence of a heat sink, the LED device temperature is driven up resulting in lower performance and lifetime.